Burping cows and sheep are being targeted by UK scientists to help bring down Britain's soaring levels of greenhouse gas pollution. Experts at the Institute of Grassland and Environmental Research in Aberystwyth say the diet of farmed animals can be changed to make them produce less methane, a more potent global warming gas than carbon dioxide. Farmed ruminant animals are thought to be responsible for up to a quarter of "man-made" methane emissions worldwide though, contrary to common belief, most gas emerges from their front, not rear, ends.

Mike Abberton, a scientist at the institute, said farmers could help tackle climate change by growing grass varieties bred to have high sugar levels, white clover and birdsfoot trefoil, a leafy legume, for their animals to eat. The altered diet changes the way that bacteria in the stomachs of the animals break down plant material into waste gas, he said. The institute has started a new government research programme, with the universities of Wales and Reading, to investigate how this process could be improved. A similar project in New Zealand suggested that dietary changes could reduce methane emissions from sheep by up to 50%.

Dr Abberton said: "It's very unlikely that we'll get that sort of reduction in the UK but it could still make a significant difference. Making the animals' diet more digestible can lower their methane emissions." A single cow can produce between 100 and 200 litres of methane every day. Farmers regularly re-sow their fields so Dr Abberton said the switch in diet could be relatively straightforward. Birdsfoot trefoil can be difficult to grow, he said, but part of the new project is to develop more suitable varieties.

As well as helping to reduce methane production, growing legumes such as clover could help replenish soil nitrogen levels because they naturally attract bacteria and fungi that fix it from the air. In a separate project, Giles Oldroyd, a plant scientist at the John Innes Centre in Norwich, is working on ways to genetically modify other plants such as wheat so they can mimic this nitrogen-fixing ability, an advance he called the holy grail of crop research because it would dramatically cut the use of synthetic fertilisers.

Scientists at the University of Hohenheim in Stuttgart, Germany, announced this year that they had developed a pill to reduce methane emissions from cattle. The plant-based pill, combined with a special diet and strict feeding times, is meant to reduce the methane produced by cows by converting it to glucose.